Electric charging method

ABSTRACT

Apparatus for uniformly charging the surface of an insulating member by first charging a portion of the surface to a magnitude smaller than the desired amount of charge by a first charging electrode. The amount of charge thus deposited is subsequently detected and compared with the desired amount of charge to be deposited. As a result of the comparison, a second charging electrode, spaced apart from the first charging electrode, is energized whereby the total charge applied to the portion of the insulating member previously charged is substantially equal to the desired amount of charge.

United States Patent Matsumoto et a1.

[4 1 July 18,1972

[541 ELECTRIC CHARGING METHOD [72] Inventors: Seljl Matsumoto; MlsamlchlSato; Osamu Fukushlma, all of Asaki, Japan [73] Assignee: XeroxCorporation, Stamford, Conn.

[22] Filed: April 19, 1971 [211 Appl. No.: 134,940

[52] US. Cl ..317/262 A, 250/49.5 ZC [51] Int. Cl. ..1-l0lt 19/00 [58]Field of Search ..317/262 A; 250/49.5 GC, 49.5 ZC

[ 56] References Cited UNITED STATES PATENTS 3,586,908 6/1971 Vosteen..317/262 A 3,582,731 6/1971 Scto et a1. ..317/262 A 3,604,925 9/1971Snelling ..317/262 A 3,013,203 12/1961 Allen et al. ..250/49.5 ZC

Primary Examiner-J. D. Miller Assistant Examiner-Harry E. Moose, Jr.

Attorney-James J. Ralabate, Albert A. Mahassel, John E. Beck and IrvingKeschner ABSTRACT Apparatus for uniformly charging the surface of aninsulating member by first charging a portion of the surface to amagnitude smaller than the desired amount of charge by a first chargingelectrode. The amount of charge thus deposited is subsequently detectedand compared with the desired amount of charge to be deposited. As aresult of the comparison, a second charging electrode, spaced apart fromthe first charging electrode, is energized whereby the total chargeapplied to the portion of the insulating member previously charged issubstantially equal to the desired amount of charge.

4 Claim, 4 Drawing Figures PATENIED JUL! 8 I972 SHEET 1 BF 2 INVENTORKSEIJI MATSUMOTO MASAMICHI SATO HY OSAMU FUKUSHIMA ORMEY PATENIEU JUL18I912 SHEET 2 BF 2 I TO CORONA DISCHARGE ELECTRODE l2 BACKGROUND OF THEINVENTION In the art of electrophotography, an electrophotographicmaterial comprising a photoconductive insulating layer on anelectroconductive base is electrically charged generally by means ofcorona discharge, the charged material is exposed to light from an imageand subsequently electrically charged particles are depositedselectively thereon so as to produce a visible image. When theelectrophotographic material is subjected to electric charging, theamount of electric charge deposited on the material varies with theconditions associated with the corona discharge, such as relativehumidity, contamination of the charging electrode, etc. or with thevariation of the distance between the corona discharge electrode and thesurface of the electrophotographic material to be electrically charged.In particular, where sufficient electric charging is to be accomplishedin a short period of time, variation in the voltage being applied to thecorona discharge electrode has its efiect manifested in the variation ofrelative speed when the electrophotographic material and the coronadischarge electrode are in relative motion.

SUMMARY OF THE INVENTION The present invention relates to chargingapparatus for minimizing the variation in the amount of electric chargedeposited on an insulating surface. In particular, the surface of theinsulating material is charged to a magnitude smaller than the desiredamount of charge by a first charging electrode. The amount of electriccharge deposited is subsequently detected and a signal correspondingthereto is coupled to a comparison means which generates a signalproportional to the difference between the detected signal and a signalcorresponding to the desired amount of charge. The difference signal iscoupled to a second charging electrode spaced apart from the firstcharging electrode which generates an electric charge of a magnitude tobring the total charge applied to the surface of the insulating materialsubstantially equal to the desired amount of charge.

It is an object of the present invention to provide novel apparatus foruniformly charging the surface of an insulating material. I

It is a further object of the present invention to provide novel methodand apparatus for uniformly charging the surface of anelectrophotographic material.

It is still a further object of the present invention to uniformlycharge the surface of an insulating material by first charging thesurface to a magnitude smaller than the desired amount of charge by afirst charging electrode. The amount of charge is subsequently detectedand compared with the desired amount of charge to be deposited. As aresult of the comparison, a second charging electrode, spaced apart fromthe first charging electrode, is energized whereby the total chargeapplied to the insulating surface is substantially equal to the desiredamount of charge.

DESCRIPTION OF THE DRAWING For a better understanding of the inventionas well as other objects and further features thereof, reference is madeto the following description which is to be read in conjunction with theaccompanying drawings wherein:

FIG. 1 is a block diagram of apparatus for use in a first embodiment ofthe present invention;

FIG. 2 is a block diagram of apparatus for use in a second embodiment ofthe present invention;

FIG. 3 is the power source and comparison means for the adjustablecorona discharge electrode; and

FIG. 4 is a third embodiment of apparatus utilized in the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, aphotoconductive insulating layer 1, obtained for example by mixing zincoxide powder with an insulating resin such as silicone resin, is formedon a conduc tive base member 2, made for example of a paper processed soas to acquire electroconductivity or a resin film having a conductivematerial vacuum deposited thereon, forming a photoconductive insulatingmember mounted on support 3. The support 3 is capable of movement in thedirection of arrow 4. A plurality of corona discharge electrodes, orwires, 5 are partially enclosed by shield case 6. A high voltage powersource 7 from about 3 KV to approximately 10 KV in magnitude is appliedto corona wires 5, the photoconductive insulating layer 1 beingelectrically charged in an amount approximately 50 percent of thedesired magnitude of chargefl'A detecting head 8 for detecting thesurface potential of the portion of the insulating layer 1 which hasbeen charged by the first corona wires 5 is connected to surfaceelectrometer 9, the output thereof being connected to delay circuit 10.The output of delay circuit 10 is coupled to a second corona dischargeelectrode, or wire, 12 via a high voltage power source 11. It ispreferred to retain the charging efficiency of the second coronadischarge electrode 12 less than that of the first corona dischargeelectrode 5. It is possible to control charging efficiency bycontrolling the distance between the corona discharge electrode and thesurface of the insulating member, the distance preferably being in therange from about 10 to about 50 mm. The surface potential detected byhead 8 is transmitted as an electric signal and displayed on the surfaceelectrometer 9. This electric signal is so delayed by delay circuit 10as to cause the second corona wire 12 to be energized when the portionof the surface of insulating layer 1 at which the correspondingdetection was made by the head 8 has advanced and arrived directly belowthe second corona discharge wire 12. At the same time the delayed signalcauses the voltage applied to the second corona discharge wire 12 to bechanged in proportion to the difference of the detected charge from thedesired surface charge. The power source 11 for generating a variablevoltage dependent upon the difference in detected charge is describedhereinbelow with reference to FIG. 3. If, for example, the potentialapplied to the second corona wire 12 from the'high voltage power source1 1 increases with the increasing difference between the amount ofelectric charge detected-by head 8 and the desired magnitude of electriccharge, the corona discharge generated by second corona discharge wire12 is adjusted to being the amount of electric charge at the detectedportion of the photoconductive insulating layer 1 to the desiredmagnitude of charge. Where the difference is small, the potential to beapplied to the second corona wire 12 is lowered proportionally. Thus,possible dispersion in the amount of electric charge deposited on thesurface of insulating layer 1 is decreased.

FIG. 2 illustrates another embodiment of the present invention. Thisembodiment is similar to that illustrated in FIG. 1, except thephotoconductive insulating material is in the form of a roll ofsensitive paper which is driven in the direction of arrow 4 on support3. A screen grid 13 for controlling the amount of corona discharge bythe first corona wires 5 and screen grid 14 for the second corona wire12 are also illustrated. A power source 15 is used to apply a fixedpotential to' the screen grid 13. By disposing screen grid 13 at a fixedpotential adjacent corona wires 5, it becomes possible to carry outstable corona discharge and consequent uniform electric charging.Further, screen grid 14 serves to facilitate the control of the coronadischarge of the second corona wire 12. When the potential applied tothe second corona wire 12 is changed, a heavy change in the amount ofcorona discharge may result, making it rather difiicult to obtainuniform electric charging. Simple control can be achieved for making thenecessary increase of the amount of electric charge by increasing thepotential of the power source 11 in accordance with the signals detectedby head 8 and, at the same time, lowering the potential of the powersource 16 for the screen grid 14. The amount of corona discharge canalso be changed by varying the potential applied to screen grid 14without changing the potential applied to the second corona wire 12.Sensitive paper 1 may be driven continuously or intermittently,whichever is preferred.

FIG. 3 shows an embodiment of an adjustable power source for the secondcorona discharge electrode 12. A fixed voltage source 17 is coupled toone input of operational amplifier 18, the output thereof beingconnected to motor 19. A high voltage transformer 20, having primary andsecondary coils 21 and 22, respectively, has its primary coil connectedto power source 23. The signal from delay circuit is compared with thevoltage generated by fixed power source 17, corresponding to the desiredamount of charge, in operational amplifier 18. The primary coil 21 ofhigh voltage transformer 20, excited by power source 23, induces a highvoltage in secondary coil 22. The position of a tap on the primary coil21 is controlled by motor 19, and where the measured surface charge orpotential, is less than the desired value, the tap is moved in adirection to increase the coil rate (number of coils) in the primary,thereby increasing the voltage at the secondary coil 22. Alternatively,if the measured surface potential is too large, the coil rate may bedecreased by moving the position of the tap in the opposite directionthereby decreasing the secondary voltage. The voltage at the secondaryside of high voltage transformer is transformed to a direct current by arectifying circuit comprising diode 24 and capacitor 25, the output ofthe rectifying circuit being connected to the secondary corona dischargeelectrode 12.

In the embodiments shown in FIGS. 1 and 2, the amount of electric chargedeposited on the insulating surface is controlled by regulating theamount of corona discharge. Altematively, the amount of electric chargecan be varied by controlling the distance between the corona dischargeelectrode and the surface of the insulating member to be charged bylessening this distance for an increased amount of electric charge andincreasing the distance for adecreased amount of electric charge. Thisembodiment is shown in FIG. 4. With the apparatus shown in FIG. 4, thecharge generated by the secondary corona discharge electrode 12 iscontrolled by actuating the electrode either towards or away from thesurface of insulating layer 1. The motor 19, shown in FIG. 3, in thisembodiment is controlled by operational amplifier 18 and drives an arm20 in response to the difference in the measured surface potential. Thearm 20 is coupled to the shield partially enclosing the electrode 12,the secondary corona discharge electrode 12 being driven up and down asarm 20 rotates about pivot point 27. The rotation of motor 19 can becommunicated to the arm 20 by means of a link system and/or wire (notshown). As set forth hereinabove, the charge value is increased when thecorona discharge electrode approaches the surface of insulating layer 1and is decreased when the electrode moves away from it. Accordingly,motor 19 actuates arm' 20 to move the secondary corona dischargeelectrode 12 away from insulating layer 1 when the surface potentialmeasured by detector 8 is too large, and to move electrode 12 towardsthe surface when too small. In this case, the voltage applied tosecondary corona discharge electrode 12 may be of a fixed value such asthat applied by source 26, and the high voltage transformer circuitshown in FIG. 3 would not be required.

The voltage applied to the first and second corona discharge 7electrodes may be of direct current. Alternatively, direct and alternatecurrents may be used together.

Although the embodiments described hereinabove only Although the memberto be charged has been generally characterized as an electrophotographiclayer overlying a conductor, the present invention may be utilized withequal facility with an electrically insulating material formed on aconductive support. For example, a layer of plastic formed on aconductive support may be uniformly and efficiently charged with theapparatus of the present invention.

While the invention has been described with reference to its preferredembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventionwithout departing from its essential teachings.

What is claimed is:

1. Apparatus for uniformly charging the surface of an insulating memberto a predetermined charge magnitude comprising:

means for charging a portion of said insulating member to a chargemagnitude less than said predetermined charge magnitude by a firstcorona discharge electrode, means for transporting said charged portionof said insulating member towards a second corona discharge electrodespaced-apart from said first corona discharge electrode,

means for generating a signal representing the amount of chargedeposited on said insulating member portion as said charged portionmoves toward said second spacedapart corona discharge electrode,

means for delaying said generated sigrnal for a time sufficient toenable said charged portion of said insulating member to be charged bysaid second corona discharge electrode,

means for comparing said delayed generated signal with a signalrepresenting said predetermined charge magnitude and generating adifi'erent signal as a result thereof, and means for applying saiddifference signal to said second corona discharge electrode whereby thecharged portion of said insulating member is charged substantiallyuniformly to said predetermined charge magnitude.

2. Apparatus as defined in claim 1 wherein screen grids are disposedbetween said corona discharge electrodes and the surface of saidinsulating member.

3. Apparatus as defined in claim 2 wherein said delayed signal isapplied to the screen grid adjacent to said second corona dischargeelectrode whereby the amount of charge generated thereby is controlled.

4. Apparatus for uniformly charging the surface of an insulating memberto a predetermined charge magnitude comprising:

means for charging a portion of said insulating member to a chargemagnitude less than said predetermined charge magnitude by a firstcorona discharge electrode, means for transporting said charged portionof said insulating member towards a second corona discharge electrodespaced-apart from said first corona discharge electrode,

means for generating a signal representing the amount of chargedeposited on said insulating member portion as said charged portionmoves toward said second spacedapart corona discharge electrode,

means for delaying said generated signal for a time suffrcient to enablesaid charged portion of said insulating member to be charged by saidsecond corona discharge electrode,

means for comparing said delayed generated signal with a signalrepresenting said predetermined charge magrnitude and generating adifierence signal as a result thereof, and means for applying saiddifference signal to a movable member, said movable member moving saidsecond corona discharge electrode towards and away from the surface ofsaid insulating member in accordance with said difi'erence signal,whereby the charged portion of said insulating member is chargedsubstantially uniformly to said predetermined charge magnitude.

1. Apparatus for uniformly charging the surface of an insulating memberto a predetermined charge magnitude comprising: means for charging aportion of said insulating member to a charge magnitude less than saidpredetermined charge magnitude by a first corona discharge electrode,means for transporting said charged portion of said insulating membertowards a second corona discharge electrode spaced-apart from said firstcorona discharge electrode, means for generating a signal representingthe amount of charge deposited on said insulating member portion as saidcharged portion moves toward said second spaced-apart corona dischargeelectrode, means for delaying said generated signal for a timesufficient to enable said charged portion of said insulating member tobe charged by said second corona discharge electrode, means forcomparing said delayed generated signal with a signal representing saidpredetermined charge magnitude and generating a different signal as aresult thereof, and means for applying said difference signal to saidsecond corona discharge electrode whereby the charged portion of saidinsulating member is charged substantially uniformly to saidpredetermined charge magnitude.
 2. Apparatus as defined in claim 1wherein screen grids are disposed between said corona dischargeelectrodes and the surface of said insulating member.
 3. Apparatus asdefined in claim 2 wherein said delayed signal is applied to the screengrid adjacent to said second corona discharge electrode whereby theamount of charge generated thereby is controlled.
 4. Apparatus foruniformly charging the surface Of an insulating member to apredetermined charge magnitude comprising: means for charging a portionof said insulating member to a charge magnitude less than saidpredetermined charge magnitude by a first corona discharge electrode,means for transporting said charged portion of said insulating membertowards a second corona discharge electrode spaced-apart from said firstcorona discharge electrode, means for generating a signal representingthe amount of charge deposited on said insulating member portion as saidcharged portion moves toward said second spaced-apart corona dischargeelectrode, means for delaying said generated signal for a timesufficient to enable said charged portion of said insulating member tobe charged by said second corona discharge electrode, means forcomparing said delayed generated signal with a signal representing saidpredetermined charge magnitude and generating a difference signal as aresult thereof, and means for applying said difference signal to amovable member, said movable member moving said second corona dischargeelectrode towards and away from the surface of said insulating member inaccordance with said difference signal, whereby the charged portion ofsaid insulating member is charged substantially uniformly to saidpredetermined charge magnitude.